A successive approximation type AD converter is known as an analog-to-digital converter (hereinafter described as “AD converter” or “ADC”). In a wireless communication device that includes an AD converter in a receiver, a harmonic of a clock signal used at the AD converter becomes an extraneous emission (spurious emission). The spurious emission in a frequency band of a received radio-frequency (RF) signal may sometimes cause noise and degrade reception sensitivity of the radio-frequency signal.